Computer data to be stored on removable media is typically arranged in data volume units that originally corresponded to one data storage media, such as a reel of tape or tape cartridge or cassette, or an optical disk or cartridge. The capacity of such storage media has grown substantially in recent years. Thus, the average size of data sets in most computer or data processing centers is significantly less than the capacity of the data storage media volumes. Most programming support for peripheral data storage is directed at only the original volume units and does not provide a general solution to storing multiple data sets in the same volume. Consequently, the potential capacity of removable data storage volumes is not realized because a single small data set is stored in one volume, leaving the remainder of the volume unused. It will be appreciated that in an automated storage and retrieval library, the cost of the system includes the cost of the unused media as well as the cost of storing the unused portion in the library.
A recent development for better utilizing the full capacity of a removable media cartridge (also called a media volume or a physical volume) is to store multiple volumes (called virtual or logical volumes) on a single physical volume. Data which would have been stored in multiple, mostly unused physical volumes are collected and stored on a single physical volume in separately addressable, host-processor defined logical data storage volumes. Both the '557 patent and the coassigned application describe the creation and management of such logical volumes and the associated physical volumes in an automated virtual storage and retrieval library. As the result, the host processor treats only logical volumes as though they were separate physical media volumes, and the library manages the access to the logical volumes by accessing the associated physical volumes: A subsystem providing automatic management of tape data storage having such logical volumes is called a Virtual Tape Server. As can be appreciated, the management of contention for disparate logical volumes on the same physical volume can be very difficult. The documents incorporated by reference are directed to providing solutions to these problems by such a Virtual Tape Server. The patents describe establishment of a stored table of logical volume records and of physical volume records for managing the data storage.
A helpful tool in managing the massive numbers of logical volumes that can be stored in such libraries is the concept of "Categories". As described in the '557 patent, a category may be defined for data storage volumes having a common attribute. Some common attributes include scratch volumes, expiration dates, common user, type of volume, host-processor data related to a job or set of jobs, volumes to be transferred or migrated to a scratch category, etc. A set of logical volumes may be selected for use by calling for a category, which will select any volume in the category. One example is mounting one volume from a scratch category on a drive of the library.
Presently, the average number of logical volumes contained in a single physical volume is approximately 50. The number of cartridges in a typical tape library is 1,000, with the result that a typical Virtual Tape Server tape library, such as the IBM 3494, contains 50,000 logical volumes. A library initially containing empty cartridges will gradually add data and fill the physical volumes with logical volumes as described in the '557 patent. In addition, some cartridges will be taken offline, out of the library and placed in shelf storage, and be replaced by new cartridges. Also, some data will be replaced or reorganized such that cartridges will become available for reuse as though new. Management of the data storage table for tracking the logical and physical volumes is accomplished by the Virtual Tape Server.
On occasion, the library may be reconfigured by expansion, shrinkage, repair, addition of drives or of a large group cartridges. In such instances, the library cannot gradually accomplish a corresponding reconfiguration of the data storage table, and the host has no way of tracking the physical and logical volumes stored in the library. Thus, the library must be taken offline and be reinventoried.
Each physical or logical volume that is inventoried requires a finite amount of time to be added to the inventory. The large number of physical volumes and the much larger number of logical volumes require that the library be offline and unavailable for use an unacceptable length of time while the new inventory is made and is uploaded to the host processor.
What is required is a way of shortcutting the inventory process, and allowing the library to be back on line and available for use much sooner than previously possible.